The present invention relates to fluid flow testing in subterranean hydrocarbon wells. More particularly, the present invention relates to methods and apparatus for flow testing in open-hole wells in unconsolidated formations.
Whether at sea or on land, during testing and completion of hydrocarbon wells, it is often necessary to test or evaluate the production capabilities of a well. This is typically done by isolating a subsurface formation, or a portion thereof, which is to be tested and subsequently flowing a sample of well fluid up through a tubing string to the surface. Various well data, such as pressure and temperature, in both static and flow conditions, may be monitored to evaluate the long-term production characteristics of the formation.
In a consolidated formation, where the formation materials provide well bore integrity such that the risk of collapse of the well bore is low, it may not be necessary to case the well bore prior to performing a drill stem test. Consolidated formations are often formed of hard rock, such as dolomite or limestone. In a consolidated well, open-hole packers are set directly against the well bore walls to isolate the zone of interest. Subsequently, the well is flow tested in the tubing string. A drill stem test tubing string carries packers, tester valves, circulating valves and the like to control the flow of fluids through the tubing string.
In an unconsolidated formation the risk of collapse of the well bore is high. Such a formation is typically formed of sand, or sand-and-shale, materials. Typically, where an unconsolidated well bore collapses onto the tubing string, it is not possible to obtain good test data. Consequently, one commonly used well testing procedure in unconsolidated wells is to first cement a casing into the well bore, perforate the casing, and then to perform the testing adjacent to the zone of interest in the formation. Subsequently the well fluid is flowed through perforations in the casing.
Although fluid flow testing of cased wells provides good test data, it has the disadvantage that the well must first be cased before the test can be conducted. Setting casing is costly and time-consuming. In xe2x80x9cthrow-awayxe2x80x9d wells, which are drilled primarily only for verification purposes, it is particularly desired to eliminate or lower total well costs. Also, better reservoir data can be obtained immediately after the well is drilled, prior to casing the well and before the well bore is damaged by drilling fluids and the like. This has led to a number of attempts at developing a successful open-hole test which can be used in an unconsolidated bore hole.
The invention comprises a tubing assembly for use in testing an unconsolidated open-hole portion of a well bore located below a cased portion of the well bore. The tubing assembly comprises an elongated tubing string extending from a well surface into the unconsolidated open-hole portion of the open hole, an open-hole packer mounted on the tubing string for use in sealingly engaging the unconsolidated open-hole portion of the well bore, a casing packer mounted on the tubing string between the open-hole packer and the well surface for sealingly engaging the cased portion of the well bore and a sand control device connected to the tubing string below the open-hole packer. The assembly may further comprise additional open-hole packers and sand control devices mounted on the tubing string. The tubing string may additionally have a data acquisition instrument mounted to the tubing string.
The open-hole packer and sand control device may be retrievable. The assembly may have one or more tubing disconnects mounted to the tubing string to disconnect segments of the tubing assembly. A tubing disconnect may be mounted to the tubing string between the open-hole packer and the sand control device or between the open-hole packer and the casing packer. The tubing string may further comprise a selective flow device for selectively controlling the flow of well fluids from the well bore into the tubing string. These devices may be controlled from the surface, activated by acoustic telemetry, or by surface intervention, by wireline or coil tubing.
Another aspect of the invention comprises a subterranean well having a well bore with a well surface, the subterranean well comprising a cased portion along at least a length of the well bore, an open-hole portion along at least a length of the well bore below the cased portion, and a tubing string assembly positioned in the well bore, the tubing assembly comprising: a length of tubing extending from the well surface to the open-hole portion of the well bore, a casing packer connected to the tubing for sealingly engaging the cased portion of the well bore, an open-hole packer connected to the tubing for sealingly engaging the open-hole portion of the well bore and a sand control device connected to the tubing.
The method of performing a flow test in a well bore in an unconsolidated subterranean formation, the well bore having a cased portion above an open-hole portion, comprises the steps of running a tubing assembly into the well bore, the tubing assembly comprising tubing, a casing packer mounted thereon, an open-hole packer mounted on the tubing downhole from the casing packer and a sand control device mounted on the tubing downhole from the open-hole packer; setting the casing packer in the cased portion of the well bore; setting the open-hole packer in the open-hole portion of the well bore; and selectively flowing fluids from the unconsolidated formation through the sand control device and into the tubing assembly to conduct the flow test.
The method may further comprise the steps of measuring well data, retrieving at least a segment of the tubing assembly, and disconnecting at least a segment of the tubing assembly. In the method, the tubing assembly may further comprise another open-hole packer mounted on the tubing downhole of the sand control device and another sand control device mounted to the tubing downhole of the another open-hole packer. The step of selectively flowing fluids may include selectively flowing fluids through the multiple sand control devices.